Electrostatic recording and reproducing



y 14, 1940- F. GRAY 2,200,741

ELECTROSTATIC RECORDING AND REPRODUCING Filed May 1, 1937 lNl EN 70/? f. GRA r A TTOR/VE V Patented May I4, 194% v V I a V UNI TED 'STA T-E'S PAT ENT OFFICE Y ELEcTltb snTgr'lggfil-lccglgnNG AND Frank Gray, New York, N Y; assignmto Bell Telephone lnw 'mtl-ted, New

York, N. Y., a of New York 1 Application May 1, 1931; lilo-140,111

suaim lclrns mai w This application relates to electric-signaling ,atedmnd accordance with incomandmore-specific'ally to the electrostatic record-- ing this embodiment the charged 'ing of signals. r tape is adapted past but not to touch a An object of this'invention is to provide novel metallic element,-shielded-from all but a narrow 5 methods of and apparatuszfor theJelectrostatic .aIea'oIthistape-by asuitable shield. in order to I recordingof signals;- 1

l reproduce by electrostatic induction the signals 5' "Several methods. of recording signals electrosuccessively positioned uponthe tape. A'feature statically have been proposed before. None of of the preferredembodiment is'that no contacts these systems, however, possesses. the flexibility, are provided-which mechanically touch this tape f accuracy and speedof the well-known'method of eitherinrecording or reproducing stages 10 electromagnetic recording i as performed by the although there maybe provided a guidefor the telegraphone. In the present invention, an electape in the recording stage which may be placed ;ftiostatic method of recording is provided which at a suitable positive potential above ground."

is fully as flexible as the telegraphone andin The invention will be more'readily understood addition possesses several advantages thereover. by referringto the following descriptlon taken in 1 For example, because of the fact that there are connection Y with. the accompanying drawing no magnetic coils in either the recording 'or forming a part thereof in which: reproducing stages of this method, there is no Fig. 1 is a schematic diagram of an electrostatic consequent shift in phase between the input and recording and reproducing system; I

no output signals. This shift in phase in the case Fig. 2 is a cross-section of a portion of the film a of a telegraphone offers very serious objections used in the system of Fig. 1; and in a situation where it is desired to record and Fig. 3 is a. schematic diagram of a modified reproduce television signals. In the case of the electrostatic recording and reproducing system. telegraphone, the constant shift-in phase angle Referring more particularly to the drawing,

will not be a constant shift in time for the.vari- Fig. 1 shows schematically an electrostatic re- I ous frequencies making up the composite telecording and reproducing system; The system vision signal, a factor which will cause much dis- 7 comprises a dielectric tape it (see Fig. 2) of suittortion in the final television image. For examable insulating material H, such as forexample pie, 2. shift of 90 degrees is a shift in time of Cellophane,- coated on one side with a thin layer,

th of a second for a. 1500-cycle component or coating 'of'a suitable conducting material, so but only lg th of a second'for a 20-"cycle composuch :as carbon, which iscaused to pass between nent. This angular shift is also accompanied by contacts i3 and .l in the'recording stage and a loss in amplitude at the lower frequencies, thus between contacts 45 and it in the reproducing introducing more distortion.- The present sysstage. The film is unwound from a roller I1 tern ofiers'further advantages in that it is simple and wound again on a roller It, the film being a; to construct, easy to operate, andcomparatively wound and'unwound at any desired speed by any cheap. 3 V suitable means not shown). The desired speed.

In one embodiment of the invention, there would, of course, bedetermined by the frequency provided an. electrostatic recordingand reproof "the incoming signals which are applied beducing system comprising Ta; film ofinsulating tween the contacts 1 3 and II by means of a trans- 4o y ateri rsucn as, for example, Cellophanqhavformer is having a p m winding 0 and a ing on one'side a-coating-of suitable conducting secondarywinding. 2|. Contact I 4 is preferably material, such as carbon, afpair of contacts beconnected to ground andv a direct current bias is tween which thejfim' passes to receive ele'ctroapplied to contact l3 by means of a source of static charges proportional tos'i'gnalsfapplied bedirect'current potential 22.

*tween these contacts,- and a set of reproducing As the movingdielectric'tape passes between contacts; through which the film is later caused contacts I31 and ,an electrostatic charge is imto l-pjasa' which are connected in'the-inp'ut circuit parted thereto. As the metallic coating I2 (see of a mplifying device in the reproducing cir- Fig. 2) is in contact with the contact member l4 cultlna modification (which is a preferred a char e. is laid o the front surface f them embodiment of-.this'invention), the electrostatic insulating fi l,- Whlch proportional to charges areapplie'd to. the dielectric tape by changes in the signal in the primary winding 20 means of a. modulated electron beam which, is of the transformer It, the film |l'- acting as a caused to pass through'an aluminum .window in dielectric forthis purpose. Due to the high 55, a cathode ray devicein which the beam is generspecific resistance of the material comprising the II film ii there is little or no surface leakage to distort the signal.

A predetermined interval of time after a succession of charges have been imparted to successive elemental lengths of the tape or film ill as described above, this interval being determined by the length of the film between the contacts l3 and i4 and the contacts i5 and i6 and'the speed of the film between these two points, the tape is caused to pass between the contacts I6 and i6 for the removal of the charge. As the tape l0 passes between the contacts i5 and IS a difference of potential is imparted to the input electrodes including the grid 23 and the cathode 24 of the vacuum tube amplifying device 25. The input circuit includes the customary coupling condenser 26, input resistor 21 and biasing battery 28. The amplifying device 25 may represent one or more stages of amplification and the output of this amplifying device may be conducted to any suitable translating device such as, for example, a telephone receiver, a loud-speaker or a television receiving device. Due to the fact that both recording and reproducing stages are electrostatic rather than electromagnetic, the phase relation of the current in the output circuit is substantially the same as that of the current in the input circuit, thus materially limiting the distortion in certain types of signals as, for example, television or picture transmission signals wherein a non-uniform shift in time between signal components of different frequencies (caused by a constant angular shift) may introduce serious distortion.

A second embodiment of this invention, which may be considered as the preferred embodiment, is disclosed in Fig, 3. In the system shown in this figure, the secondary winding 2| of the transformer I9 is connected in circuit with the cathode 30 and the modulating element 3i of a cathode ray device 32. The cathode ray device 32 has means, such as the cathode 30 and an accelerating anode 33, for forming an electron beam and for accelerating it toward the end wall 34 of the tube. The end wall 34 has an aperture 36 therein which is covered with a thin strip 36 of aluminum thus forming in the end wall 34 a narrow aluminum window. Aligned with this window is a guide member 31 which is preferably connected through a source 38 to ground. This source thus applies as positive potential to the guide number 31 with respect to ground.

The tube 32 is preferably made in two portions; a glass portion 39 enclosing the electron gun apparatus and a copper portion 40 which is sealed to the glass portion 39 so as to make a composite tube. In the preparation of the seal between the glass tube 35 and the metallic tube 40, the copper tube 40 is drawn out into a sharp edge indicated at 4|, the reduction preferably being tapered so that the taper extends from 5 of an inch to A of an inch backward from the end of the tube. A section of the tapered tube 39 is fitted inside the copper tube adjacent the reduced portion U of the copper tube, the copper tube being'held in a suitable fixture. The copper and glass tubes at the point of contact are then heated above the melting point of the glass to fuse the two together in a tight joint. For a complete description of the method of sealing glass and copper tubes briefly described above, reference may be made to Patent 1,294,466, issued February 18, 1919, to W. G. Houskeeper.

Cathode 30 is heated by heating means such as the filament 42 supplied with current from a source of potential 43. The first acceleratin anode 33 is placed at a positive potential with respect to the cathode 30 by means of a source of direct current potential, such as the battery 44. The copper tube 40 serves as a second accelerating and focussing member and is positively biased with respect to the accelerating anode 33 by means of a suitable source of direct current potential, such as the battery 45. The tube 40 is preferably connected to ground.

' Instead of making direct contact between the tape II and a reading element, when reproducing the signals, an inductive method of reading may be used. In this modification, the charged tape I I runs past but does not touch the metallic element 46 which is shielded from all but a narrow area of the tape ill by a shield 41 having a small aperture 48 therein which is just sufficient to accommodate the metallic member 46 without touching it. Connections from the shield 41 and the metallic element 46 are made through a coupling condenser 26 to the input circuit of the amplifying device 25, this input circuit being otherwise as described above with reference to the reproducing circuit shown in Fig. 1.

The operation of the electrostatic recording and reproducing system shown in Fig. 3 will now be described. An electron beam is generated by the cathode 30 and accelerated and focussed by means of the accelerating anode 33 and the copper tube 40 so that a narrow beam of high velocity is directed towards the aluminum window 36 in the tube 40. Due to the high velocity of the electron beam, charged particles pass through the aluminum window and apply charges to the moving tape i0 which are proportional to changes in the intensity of the incoming signal used to modulate the electron beam by means of the modulating element 3|. The means to move and guide the tape in its path may be as described above with reference to Fig. 1. As the electrons in the beam are negatively charged, the aluminum window is at ground potential and the guide member 31 at a high positive potential, a charge is imparted to each of the successive elemental areas of the moving film III which is held on that particular elemental area by means of the high specific resistance and the high dielectric constant of the insulating material II comprising the film I 0. The device is operative if the contact and guide member 31 and the battery 38 are not used. A certain predetermined time after the charge corresponding to a specific signal has been applied to the tape i0 this specific elemental charged area passes opposite the metallic reproducing element 46 inducing an electrostatic charge thereon. The potential differences between element 46 and the grounded shield 41 may be amplified by means of an amplifying device 25 which may comprise one or more stages as in the similar amplifying device shown in Fig. 1.

The recording and reproducing system shown and described in this application is particularly well suited for producing a signal time delay of short duration in, for example, systems of television, telephotography or telephony. By properly proportioning the amount of tape between the recording and reproducing element and the speed of the tape, the delay time may be controlled. The successive charges representative of the successive incoming signals, unless removed by a reproducing contact as in Fig. 1, remain on the tape for a relatively long period of time until they are removed either by wiping a metallic element, which may be grounded, across the front surface, i. e., the insulated surface of the film II], or by winding on the roll IS in such manner that the charged surface comes in contact with the metallic coating of the adjacent layer in the roll, thus dissipating the charges. The invention however is obviously not limited to the uses just mentioned. The scope of the invention in its various aspects is indicated by the appended claims, the specific embodiments described above being merely illustrative of possible means for carrying out the invention as defined by the broader claims.

While there have been described two methods of electrostatic recording and reproducing, it is obvious that this invention is not limited to these specific means as other methods of electrostatic recording and reproducing are possible within the scope of this invention. For a description of different apparatus for electrostatic recording and reproducing, reference may be made to a copending application of R. R. Riesz and H. S. Wertz, Serial No. 145,442, filed May 29, 1937.

What is claimed is:

1. A recorder and reproducer of signals comprising a film of insulating material, a conducting backing for said film, means for generating electron beam, means for modulating said beam, means causing relative movement between said electron beam and said film for imparting a varying charge to successive portions of the surface of said film remote from said conducting backing, means for applying a polarizing voltage to said conducting backing, and means for utilizing said varying charge at a later time to control the production of signals.

2. Apparatus for reproducing signals from a recording member comprising a film of insulating material having a conducting backing therefor comprising a conducting member adjacent but not in contact with said film, a shielding member for said metallic member, means for causing relative movement between said film and said metallic and shielding members, an amplifying device comprising input and output circuits, means for connecting said shielding member and said metallic member to the input circuit of said amplifying device, and means for connecting the output circuit to a translating device.

3. In combination, a moving film of insulating material having a conducting backing therefor and having varying charges applied to successive portions of the surface of said film remote from said conducting backing, a metallic member, means producing relative movement between said metallic member and said film for inducing charges in said metallic member corresponding respectively to the charges on successive portions of said film, and means for shielding said metallic member from said film except for a small portion thereof adjacent said metallic member.

4. The combination with an electrical conductor, of a conducting shield member, means for supporting saidconductor out of electric contact with said shield and with one end thereof extending through an aperture in said shield, a non-conducting element adapted to receive and retain electric charges, means for moving said element so that said charges pass consecutively adjacent to said end of said conductor, and an electric circuit terminating in said conductor and said shield respectively which utilizes said charges to control the production of signals.

5. The combination with a strip of dielectric material, of means for spraying free electrons on different portions of a continuous surface of said strip in succession, said means including a cathode ray tube having a cathode and an accelerating anode member, a conducting element in fixed relation to said electron spraying means and so positioned that said strip is between said means and said element, and means for maintaining said element positively charged with respect to said anode member. r

6. In combination, an element of insulating material, a conducting backing for said element, means under control of a variable electromotive force for imparting electric charges in succession to different portions of the surface of said element remote from said backing, said charges being of such character that they can be wiped oiT with a metal contact, means for applying a polarizing potential to said conducting backing, and means for utilizing these charges at a later time to control the production of signals.

7. In combination, an element of insulating material, a pair of metallic elements, means for causing said insulating element to pass between said pair of elements, means for positively biasing one of said-metallic elements with respect to the other, means for applying a variable voltage between said pair of elements to impart electric charges in succession to different portions of said insulating element, said charges being of such character that they can be wiped off with a metal contact, and means for utilizing these charges at a later time to control the production of signals.

8. In combination, an element of insulating material, a pair of metallic elements, means for positively biasing one of said metallic elements with respect to the other, means for applying a varying source of potential between said metallic elements, means for causing said element of insulating material to pass between said metallic elements to have surface charges applied to said insulating material in accordance with signals applied between said metallic elements, a second pair of metallic elements, an external electric circuit connected between said second pair of elements, and means for passing said charged insulating element between said second pair of elements to energize said external circuit.

9. In combination, an element of insulating material, a cathode ray device for generating a beam of electrons and for accelerating and directing said beam upon successive portions of v said insulating element, a guide member for said insulating element located on the opposite side of said element with respect to said cathode ray device, means for placing said guide member at a positive potential .with respect to that of the accelerating means of said cathode ray device,

means for modulating said. beam so that electric charges varying in accordance with signals are imparted to successive portions of said insulating element in succession, and means for utilizing these charges at a later time to control the production of signals.

FRANK GRAY. 

